Wireless or mobile (cellular) communications networks in which a mobile terminal (UE, such as a mobile handset) communicates via a radio link to a network of base stations or other wireless access points connected to a telecommunications network, have undergone rapid development through a number of generations. The initial deployment of systems using analogue signaling has been superseded by Second Generation (2G) digital systems such as Global System for Mobile communications (GSM), which typically use a radio access technology known as GSM Enhanced Data rates for GSM Evolution Radio Access Network (GERAN), combined with an improved core network.
Second generation systems have themselves been largely replaced by or augmented by Third Generation (3G) digital systems such as the Universal Mobile Telecommunications System (UMTS), which uses a Universal Terrestrial Radio Access Network (UTRAN) radio access technology and a similar core network to GSM. UMTS is specified in standards produced by 3GPP. Third generation standards provide for a greater throughput of data than is provided by second generation systems. This trend is continued with the move towards Fourth Generation (4G) systems.
3GPP design, specify and standardize technologies for mobile wireless communications networks. Specifically, 3GPP produces a series of Technical Reports (TR) and Technical Specifications (TS) that define 3GPP technologies. The focus of 3GPP is currently the specification of standards beyond 3G, and in particular on standard for the Evolved Packet Core and the enhanced radio access network called “E-UTRAN”. The E-UTRAN uses the Long Term Evolution (LTE) radio technology, which offers potentially greater capacity and additional features compared with previous standards. Despite LTE strictly referring only to the air interface, LTE is commonly used to refer to the whole system including evolved packet core (EPC) and E-UTRAN. LTE is used in this sense in the remainder of this specification, including when referring to LTE enhancements, such as LTE Advanced. LTE is an evolution of UMTS and shares certain high level components and protocols with UMTS. LTE Advanced offers still higher data rates compared to LTE and is defined by 3GPP standards releases from 3GPP Release 10 up to and including 3GPP Release 12. LTE Advanced is considered to be a 4G mobile communication system by the International Telecommunication Union (ITU).